Pulse stretcher electric circuit



NOV. 7, 1967 N 3,351,820

PULSE STRETCHER ELECTRIC CIRCUIT Filed April 21, 1964 I NVENTOR.

United States Patent 3,351,820 PULSE STRETCHER ELECTRIC CIRCUIT AndrewBalint, Park Ridge, Ill., assignor to Bell & Howell Company, Chicago,111., a corporation of Illinois Filed Apr. 21, 1964, Ser. No. 361,499 6Claims. (Cl. 317-1485) ABSTRACT OF THE DISCLOSURE responsive to thepulses. The switching means is connected to the pulse stretching circuitby meansof an input circuit having first and secondresistors and acapacitor so that closure of the normally open switch contacts willcause the capacitor to' discharge through one of the resistors and thegate of the SCR. The charge time of the capacitor and the closure timeof the'co-ntacts are such as to protect the contacts. against arcingandto insure that only a single pulse for each closure. of the contactswill be produced.

At present, the use of solenoid devices, such as relays,counter-actuators, and the like is greatly limited due to the timerequired to fully actuate such devicesQOne approach to decreasing thetime required to operate a solenoid actuating device is to decrease'the'mass of the relay armature, solenoid plunger, or the like which is to bemoved by energization of the device. A reduction in the massof such amovable component will decrease the time required to accelerate .oractuate the component; however, a point is reached where the mass can nolonger be decreased and still maintain the usefulness of, thedevice.

A further object of this invention is to provide means to increase theusable life of switching devices which are successively actuated at ahigh'rate.

, moving document makes contact with switching means Another approach todecreasing the time required to actuate a solenoid device is to increasethe power applied thereto. However, increasing the actuating power mayrequire relatively expensive components and may lead to a design whichis not economically acceptable. Also, a point is reached where anincrease in power applied to the solenoid device'has little or no effecton the timerequired to actuate the solenoid plunger or relay armature.It can be seen therefore, that this approach not only hascharacteristiclimitations, but is very costly because the cor respondingcomponents must be of a higher quality.

It is therefore an object of this invention to provide a means wherebyconventional" solenoid devices can be actuated byshort time durationpulses which would otherwise have no effect on the solenoid device.

Another object of this invention is to provide a pulse stretching devicewhich will respond to an input pulse of short time duration and providean output pulse of substantially longer time duration capable ofactuating an electromechanical load.

and will deenergize the counter while the document is still in contactwith the switching means, thereby enabling the counter to'countoverlapping documents as well as docu ments which successively followeach other.

A highly advantageous application of the invention resides in thecounting of rapidly moving documentsand a specific embodiment of theinvention for this purpose has been disclosed herein. However, it willbe apparent that the invention has a wide field of utility.

' On the drawings: T

The single figure of drawings shows a schematic diagram of a pulsestretching circuit, which is constructed in accordance with'thisinvention, and illustrates by way of example a switch means with whichthe invention may be employed.

As shown on the drawings: g

The present invention has particular utility when combined withdocument-handling apparatus utilizing a document-actuated switchingmeans comprising normally open switch contacts which are actuated inresponse to movement of sheet-like articles to develop short make-breaktime intervals which are so short as to preclude actuation of anelectromechanical device by using such pulses directly. Thus, handlingapparatus a pulse stretching circuit having an SCR with a gate electrodeand which is responsive to the pulses of short time duration to actuatethe electromechanical device. The switching means is connected to thepulse stretching circuit by means of an input circuit having first andsecond resistors and'a capacitor so that closure of the switch contactswill cause the capacitor to discharge through one of the resistors andthe gate of the SCR. The charge timeof the capacitor and the closuretime of the contacts is such as to protect the contacts against arcingand to insure that only a single pulse for each closure of the contactswill be produced. The life of such a switch will be. so extended that itwill last as long as the apparatus with which it is associated.

The pulse stretching circuitgenerally designated by reference numeral10, is rendered operative by actuation of a counting switch 11, whichhas a pair Of'bltiCtllCElllY conductive contacts 13 and 14. The contacts13 and 14 are connected through a' pair of conductors 15 and 16respectively to an input circuit 18 of a silicon controlled rectifier19. The silicon controlled rectifier 19 has connected to the anodethereof an indicating lamp 20.

In the illustrated embodiment, the actuating coil 21 of oneelectromechanical counter device is coupled to the anode of controlrectifier 19'via a diode 22. A second counter device is shown having itsactuating coil 23 connected with control rectifier 19 through a diode24. A com- Another object of this invention is to provide a means.

for counting short time duration pulses in a simple and inexpensivemanner using conventional electromechanical counters instead of usingrelativelycomplex and expensive electronic counting devices.

mutating capacitor 27 also has one terminal thereof connected to theanode of the control rectifier 19. A diode 28 is connected in parallelwith the counter 21 and in series, but of opposite conduction, with thediode 22. Adiode 29 is connected in parallel with the'counter 23 and inseries, but of opposite conduction, with the diode 24. The cathode ofcontrol rectifier 19 is connected with line731. A four layer Shockleydiode 30 has the cathode thereof connected to the, line 31, and theanode thereof there is combined with such documents connected to aresistor 32 and to the other terminal of the capacitor 27.

The silicon controlled rectifier 19 and the four layer Shockley diode 30have similar characteristics in that they are both controlledrectifiers, the main difierence being that the silicon controlledrectifier 19 has two main electrodes and a control electrode connectedthereto and the four layer Shockley diode 30 has only two mainelectrodes connected thereto. With the anode and cathode of the siliconcontrolled rectifier 19' forward biased, a signal is required at thegate electrode to switch on the silicon controlled rectifier 19.However, all that is required to switch on the four layer Shockley diodeis to have the forward bias applied thereto exceed the breakovervoltage, which is slightly less than the supply voltage.

In operation, with no counting signal from the switch 11, the four layerShockley diode 30 is conductive through resistor 32. A charging circuitfor capacitor 27 is present through the indicating lamp 20. When acounting signal, generated by the closure of contacts 13 and 14, isapplied to the input circuit 18 of the silicon controlled rectifier 19,the silicon controlled rectifier 19 is rendered conductive. Energizingcurrent then flows in parallel through the indicating lamp 20, throughthe counter 21 and diode 22, and through the counter 23 and the diode24. This current is of Sufiicient magnitude and duration to actuate thecounters represented by coils 21 and 23. The capacitor 27 applies areverse polarity voltage across the four layer Shockley diode 30 whichis thereby commutated into the non-conductive state. The capacitor 27discharges through a circuit including control rectifier 19 and resistor32 and then receives a charge of opposite polarity under the control ofresistor 32. After a predetermined time, determined by the values ofresistor 32 and capacitor 27, the capacitor 27 will become charged to avoltage nearly equal to that of the supply voltage and of polarity totend to produce conduction by the four layer Shockley diode. Thecapacitor 27 will continue to charge through resistor 32 until such timethat the voltage applied to the anode of the four layer Shockley diode30 reaches the breakover voltage thereof. At this time, the four layerShockley diode 30 is rendered conductive and the silicon controlledrectifier 19 is rendered non-conductive through the commutatingcapacitor 27 The indicating lamp 20, the counter 21 and the counter 23will then remain deenergized until the next counting signal from thecounting switch 11.

The input circuit 18, which is coupled to the gate circuit of thesilicon controlled rectifier 19, includes a resistor 35 connectedbetween the line 31 and the gate electrode of the silicon controlledrectifier 19. Also connected to the gate electrode is electricallyconductive contact 13 of switch 11. Capacitor 37 has one terminalthereof thereof connected to the line 31, and the other terminalconnected to switch contact 14 and to a resistor 39.

A transformer 40 having a primary Winding 41 and a secondary winding 42is used to decrease alternating voltage from a conventional source ofpower to the desired value for the pulse stretching circuit 10. A bridgerectifier circuit 44 has the AC terminals thereof connected to thesecondary winding 42 of the transformer 40. The DC terminals of thebridge rectifier 44 have connected thereacross a filter capacitor 46 anda bleeder resistor 47.

The counting switch 11, by way of example and not by way of limitationis of the type used in counting overlapping sheet-like articles such ascardboard cards and has three sensing arms 50, 51 and 52 fixedly securedto a triangular rotating cam 54. The sensing arms 50, 51 and 52 arearranged to extend through a panel member 55 for engagement with thecards such as indicated at 57 which move in the direction of arrow 58.The counting switch 11 may also be a snap-action switch for actuation bydocuments that successively follow each other in spaced relation.

The cards 57 each rotate the cam 54 through 120 to momentarily actuatethe contacts 13 and 14. The amount the documents can overlap isproportional to the number of sensing arms on the switch 11 andinversely proportional to the length of the sensing arms 50-52. The timeinterval between make and break of contacts 13 and 14 is very short, tooshort, in fact, to actuate the counters 21 and 23 without the use of thepulse stretching circuit. When the contacts 13 and 14 are closed bypassage of a card 57, the capacitor 37 will discharge through the gateresistor 35 of the silicon controlled rectifier 19 thereby rendering thesilicon controlled rectifier 19 conductive. Even though the contacts 13and 14 reopen after actuation thereof by the triangular rotating cam 54,the silicon controlled rectifier 19 remains conductive for apredetermined time interval such that the counters 21 and 23 areeffectively actuated. After a predetermined time, depending upon thetime constant of the capacitor 27 and resistor 32, the four layerShockley diode 30 will be rendered conductive and the silicon controlledrectifier 19 will be commutated to a non-conductive state through thecommutating capacitor 27. The diodes 28 and 29, which are connectedacross the counters 21 and 23, respectively, will act to maintain thecounters in the energized state for a period of time, for example,approximately 5 milliseconds, after the control rectifier 19 becomesnon-conductive.

By way of example only and not of limitation, a circuit as illustratedin the drawing may utilize the following components.

Part reference numeral: Illustrative component 19 Type 2N2323.

30 Type 4E208.

21, 23 IVOF108 type counters.

40 TRIAD F45X, 117 volt R.M.S. primary, 24 volt R.M.S secondary.

20 1829 lamp.

44 Type 1N537 rectifiers.

22, 23, 2 8, 29 Type 1N537 rectifiers.

47 100 ohms.

39 270,000 ohms.

35 27 ohms.

32 1500 ohms.

37 .01 microfarad.

27 6 microfarads.

46 4500 microfarads.

With a circuit having the specific illustrative components given above,the power supply provides an output of 30 volts D.C. Since the contacts13 and 14 of the switch 11 are normally open, the capacitor 37 ischarged to 30 volts through resistor 39. The four layer diode 30 isturned on and conducts through resistor 32, and the voltage across thefour layer diode at this time is about one volt. The capacitor 27 ischarged positive on the left and negative on the right, through the lamp20 and the counters 21 and 23. When the contacts 13 and 14 close,capacitor 37 discharges through the gate of the silicon controlledrectifier 19 to render the control rectifier conductive, therebyenergizing the lamp 20 and the counters 21 and 23. While the siliconcontrolled rectifier 19 is conductive, the voltage thereacross is aboutone volt which essentially grounds the left side of capacitor 27. Thecharged capacitor 27 appears briefly as a battery Whose voltage opposesthe potential through resistor 32. The

four layer diode is then turned off until the capacitor 27 dischargesthrough resistor 32 and recharges to the opposite polarity of about 20volts. At this time the four layer diode is again rendered conductiveand the charge on capacitor 27 positive on the right and negative on theleft, now opposes the voltage across the lamp 20 and the counters 21 and23. Therefore, the silicon controlled rectifier 19 is commutated off andis ready for a subsequent pulse from the sensing switch 11.

The values of resistor 32 and capacitor 27 determine the length of timethe silicon controlled rectifier is conis introduced by the shunt diodes28 and 29. The control rectifier 19 will be triggered on by each pulseand remain conductive for about '15 milliseconds after which it will beoff until the next pulse isreceivedAt theend of such a train of pulses,the counters will be deactuated after a time interval of aboutmilliseconds.

Summary of operation In operation each successive card 57 actuates thepaddle I Wheel sensing device 11 momentarilyrto close contacts 13 and14. This produces. a pulse across resistor 35 which triggers siliconcontrol rectifier 19jto a conducting state. Current then flows throughthe actuating coils 21 and 23 a said contacts against arcing andproducing only a single pulse for each closure of the contacts. 2. Theinvention ofclaim 1 wherein said pulse stretching circuit morespecifically comprises direct current power supply means for'deliveringa predetermined direct cur- I rent voltage and having'resistance meansin series thereof the electromechanical counters for a suflicient timeinterval to actuate the counters. The time interval is determined by'thetime constant of'the circuit including resistor 32 and capacitor 27. Atthe expiration 'of the selected time interval, capacitor 27 has beencharged to such a value that the four layer shockley diode301becomes'conductive; Conduction of diod'e 30 applies the voltage ofcapacitor 27 across control rectifier 19 so as to shut off the controlrectifier and thus return the circuit to its initial state in readinessfor a further pulse.

A circuit such as specifically illustrated thus comprises an electronicswitch (provided by silicon control rectifier 19) capable of respondingto pulses of a few microseconds in duration, a circuit controlled by theswitch for generating a standardized actuating pulse having a durationof the order of 15,000 microseconds, and a means (including capacitor 27and Shockley diode 30) for automatically resetting the circuit to itsinitial condition after the desired actuating time interval.

It will be understood that modifications and variations may be madewithout departing from the spirit and scope of the novel concepts ofthis invention.

I claim as my invention:

1. In combination With document handling apparatus havingdocument-actuated switching means comprising normally open switchcontacts and actuating means responsive to movement of sheet-likearticles such as documents to develop short make-break time intervals,the improvement of:

a pulse stretching circuit having a silicon controlled rectifier with agate electrode and being responsive to pulses of short time duration toactuate an electromechanical device which could not be actuated of saidresistors and having the other terminal thereof connected to a line,whereupon closure of said switch contacts said capacitor will dischargethrough said one of said resistors and the .gate of said siliconcontrolled rectifier,

the charge time of the capacitor and the closure time of the contactsbeing such as to protect with, a four layer Shockley diode connected inseries circuit with said direct current power supply means and saidresistance means, I i

. saidfour layer Shockley diode havinga breakover voltage slightly lessthan said predetermined direct current voltage, a capacitor connectedbetween said silicon cont-rolled rectifier and said four layer Shockleydiode for placing said Shockley diode in its conductive state apredetermined time] after said controlled rectifier becomes conductiveand for concurrently commutating said controlled rectifier to itsnon-conductive state in preparation for receipt of a further inputpulse,

" and means for connecting an electromechanical device in said pulsestretching circuit.

3;.The invention of claim 1 whereinsaid' actuating means comprises Varotatablecam operatively connected to said switch contacts and havingplural cam surfacesifor actuating said switch contacts and v a acorresponding plurality of sensing armsdrivingly connected tosaidcam. I4. The invention of claim 3 wherein the number of said plural sensingarms is proportional to the amount the documents can overlap and thelength of each of said I sensing arms is inversely proportional to theamount th documents can overlap.

5. A pulse actuated circuit comprising: an electromechanical devicehaving first and second terminals, 7 a silicon controlled rectifierhaving anode, cathode and gate electrodes, r saidanode being connectedto said first terminal, a source of direct current voltage having apositive terminal connected to said second terminal and a negativeterminal connected to said cathode, a first resistor, switch meanshaving one end thereof connected to one end of said first resistorforming a first circuit point, the other end of said first resistorbeing connected to the positive terminal of said source and the otherend of said switch means being connected to the negative terminal ofsaid source, a first capacitor connected between said anode'of saidsilicon controlled rectifier and the circuit point formed by said firstresistor and said switch means,

a second resistor,

to one end of said second resistor thereby forming a secondcircuit-point,

the other end of said second resistor being con nected to the positiveterminal of said source and the other end of said second capacitor beingconnected to the negative terminal of said source thereby charging saidsecond capacitor, a thirdresistor having one end thereof connected tosaid gate electrode and the other end thereof connected to the negativeterminal of said source,

and document-actuated meansincluding normally open contact membersconnected electrically between said second circuit point and'said gateelectrode and being operable upon closure by a document forsubstantially discharging said second capacitor through said thirdresistor to render said silicon controlled rectifier conductive toenergize said electromechanical device,

= the closure time of said contacts and the charging time of said secondcapacitor being such that the contacts are protected against arcing,

second capacitor having one end thereof connected 3,351,820 r I? 8 6. Apulse actuated circuit as defined in claim 5 and OTHER REFERENCESfurther characterized by the charge time of said second Survey of someCircuit Application of the Silicon capacitor through said secondresistor being in the order Controlled Switch and silicon ControlledRectifier, of 9 at least abopt loooo dlschtrge tune Applications andCircuit Design Notes, Solid State Prodof said second capacitor throughsaid third resistor. 5 ucts Inc Bulletin D December 1959 pp ReferencesCited 4, 8, 27.

UNITED STATES PATENTS MILTON o. HIRSHFIELD, Primary Examiner. 1/1966Fel'check 317148-5 L. T. HIX, Assistant Examinen 3,243,665 3/1966 Fayeret a1. 3l7148.5 10

1. IN COMBINATION WITH DOCUMENT HANDLING APPARATUS HAVINGDOCUMENT-ACTUATED SWITCHING MEANS COMPRISING NORMALLY OPEN SWITCHCONTACTS AND ACTUATING MEANS RESPONSIVE TO MOVEMENT OF SHEET-LIKEARTICLES SUCH AS DOCUMENTS TO DEVELOP SHORT MAKE-BREAK TIME INTERVALS,THE IMPROVEMENT OF: A PULSE STRETCHING CIRCUIT HAVING A SILICONCONTROLLED RECTIFIER WITH A GATE ELECTRODE AND BEING RESPONSIVE TOPULSES OF SHORT TIME DURATION TO ACTUATE AN ELECTROMECHANICAL DEVICEWHICH COULD NOT BE ACTUATED BY SAID PULSES DIRECTLY. AND AN INPUTCITCUIT CONNECTING SAID SWITCHING MEANS TO SAID PULSE STRETCHING CIRCUITAND MORE SPECIFICALLY COMPRISING: FIRST AND SECOND RESISTORS, ONE OFSAID RESISTORS BEING CONNECTED BETWEEN SAID GATE ELECTRODE OF SAIDSILICON CONTROLLED RECTIFIER AND A LINE, ONE OF SAID SWITCH CONTACTSBEING CONDUCTIVE AND BEING CONNECTED TO SAID GATE ELECTRODE, AND ACAPACITOR HAVING ONE TERMINAL CONNECTED TO THE OTHER OF SAID SWITCHCONTACTS AND TO THE OTHER OF SAID RESISTORS AND HAVING THE OTHERTERMINAL THEREOF CONNECTED TO A LINE,